You must tumbl (tumble?), or haven't you heard? You must tumbl (tumblify?) because the micro-blogging site Tumblr.com is growing fast -- its estimated 3.3 million daily visitors up 50 percent from April, according to Quantcast.com. You must tumbl (Seriously, what is the verb here?) because the early adopting tech people tell you to use Tumblr. "There's a new must-have social networking address," chirped a recent news article, and blogs offer guidance on the most "essential" tumblogs.

While you are pondering this site -- founded in 2007 but spruced up this year -- and the communication possibilities it offers, you might feel . . .

"The academic in me feels like, 'Oh, this will be interesting,' " says Zeynep Tufekci, a professor of sociology at University of Maryland Baltimore County who studies social networks. "The user in me goes, 'Oh nooo, another one!' "

There's so much social networking she has not yet accomplished. "I really wanted to dive more into the music communities, like Last.fm and Fetch . . . but that's going to be a huge investment," she says. Meanwhile, "I've been avoiding the location-based ones because they're a whole other ball of wax. It's nagging me."

At some big or small level, it's nagging all of the people who are mired enough in social networking to bother following the latest developments. This isn't everyone -- despite the fact that institutions from your local radio station to your dry cleaner beg you to follow them on Twitter, there are whole swaths of people who just don't give a flying friend request.

But consider this: At one point in their centuries-old history, the Amish were not the technological relics they are today. Everyone else was churning and buggying right along with them. At some point, electricity was invented and the Amish had to reject it. Cars were invented and they took a pass. We're good with the buggy, they said. Motoron without us.

Now, in an onslaught of sites designed to aid connection, communication and cross-promotion, individual stopping points must be declared. When will you go 21st-century Amish?

"I do Twitter; I do Facebook; I do Lawyer Connection" via Ning, says Gwynne Monahan, a legal consultant. "I did MySpace when it was popular"; now she uses it to find new music. She will not, however, do Foursquare, the network centered on virtually checking into real-life locations. That's her boundary. She doesn't have the time, and plus, "there's just no reason for people to know where I am."

On odd occasions, she wonders whether she's drawn the boundary too soon. She was visiting New York and a group of friends met up at a concert. "Everyone whipped out their phones and started checking into Foursquare" to announce their exact locations. It was easier, she admits, for some people in the group to have the application. Rather than the endless phone calls ("No, by the men's room!"), everyone immediately knew when others had arrived by their check-ins, and then everyone herded inside.

Still, the thought of plugging into yet another tool . . .

"The basic notion that people reach a technological saturation point applies to a lot of people," says Lee Rainie, the director of the Pew Research Center's Internet and American Life Project, which studies the Web's impact on society. "They literally say, enough is enough . . . and my mind is going to blow up and I can't take it anymore."

(Privacy concerns, like Monday's announcement that Facebook's most popular applications transmit personal data to marketing companies, can exacerbate already uneasy relationships with social networks.)

One problem, Rainie says, is that so many of the so-called revolutionary applications are actually riffs on a similar theme. Foursquare looks a lot like Gowalla; Tumblr could be the cousin of Posterous. It's exhausting to move onto what's new if it sort of looks like what's old. The people who still refuse to Facebook -- the most ubiquitous of them all, with upwards of 500 million members and a Quantcast-estimated 135 million daily visitors -- use this rationale: They already joined Friendster in 2004. Is that not enough? (It's worth noting that you must be a member of Facebook in order to use it, while individual Tumblr blogs can be perused by those who do not have accounts with the site.)

Will we one day be able to measure age by a person's social networks, the way one does with trees and their bark rings? Here we have a specimen who speaks MySpace, Facebook and Gowalla, but apparently stopped before Formspring.

"Everyone's on Foursquare, and everyone's on this and everyone's on that," says Xianhang Zhang, a researcher with "social design" firm Bumblebee Labs, which studies innovation and social mores. "A lot of time they don't even know why," he confides. "They just feel like they should be."

He's hearing a lot about Quora.com now, a Wikipedia-like network based on user-generated questions and answers. Quora and Hunch.com -- which recommends sites based on what you already like -- might be the next destinations the tech-savvy feel compelled to add to their personal browsing itineraries.

Part of the drive to get there first is the prestige aspect and part of it is practicality. For people who enjoy being followed, friended or otherwise Internet famous, it's easier to do so in a newer, smaller pond. At this point moving into Twitter -- which has 160 million users and an estimated 55 million daily visitors now; co-founder Evan Williams recently announced he expected it to hit 1 billion users -- is like squeezing into Georgetown, but Tumblr is a still a relatively bare plain with lots of land for homesteaders. Not only can you discover the hot new thing, but you can be the hot new thing when you get there.

"But I'm not looking for the next hot thing," says Scott Rosenberg, the co-founder of Salon.com who now blogs about technology and culture at Wordyard.com. "I do not use Foursquare. I'm a grown-up with a family. I may be missing out on some deep understanding of how geospatial awareness shapes our understanding of the world," but that's a risk he's willing to take. He'll stick with Twitter and his personal blog, thanks, and feel bad for the poor guys who are trying to sort it out. For them, "It's a challenge. Where do I put my chips? Tumblr or Posterous? Is Tumblr still going to be a big thing in the next few years?"

It's an issue of time. It's an issue of your own personal resources, and how often you want to repost the same information -- first as a status update, then as a tweet, then as a tumbl (tumblette?). It's also an issue of finding which online community feels like home.

"Each place has its own cultural norms," says Tufekci, the Baltimore professor. Just as "you would do one thing in a bar and one in thing in a church," the expectations for customizable Tumblr, in which users are precious snowflakes, are profoundly different from the expectations for the standardized Twitter. Do you want fast or slow? Individuality or hive mind? Anonymity or reciprocal relationships?

On each new site, "you're once again that awkward shy kid in the corner, and you don't know what's up. It's exactly like being a navy brat."